ryu_sh: Add Makefile in board directory.
ryu_sh: Add Makefile in board directory.

To match other boards, add a link to Makefile in board/ryu_sh.

BRANCH=ToT
TEST=compile
BUG=None

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/231983
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit 0e03ff4ad87e434a176e9e2e2b2963c9f3a83771)
Signed-off-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

Change-Id: I19c58e2fd221ddf2e607f6a732e2e6229daedd1f
Reviewed-on: https://chromium-review.googlesource.com/235724
Tested-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>
Reviewed-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>
Commit-Queue: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>
Trybot-Ready: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

thehobn/ec,thehobn/ec,thehobn/ec,thehobn/ec